Reducing mechanical anisotropy in material extrusion process using bioinspired architectured lattice structures

Additive manufacturing (AM) entails manufacturing complex lightweight structures based on the principle of layer-wise material deposition. However, this principle also results in high mechanical anisotropy in all di-rections. The process of material extrusion (MEX) is severely affected by mechanical properties owing to its processing conditions. Mechanical anisotropy can result in sudden failures when loaded multidirectionally; its effect is more predominant in lattice structures. This study was conducted to reduce mechanical anisotropy in MEX-fabricated lattice structures by mimicking the internal architecture of the human tooth. The human tooth is prone to mechanical anisotropy because the hard enamel, meant to withstand extreme mechanical forces, consists of microscopic enamel prisms (perpendicular rods). Soft dentin imbues the enamel with the necessary toughness when loaded multidirectionally. This natural design principle was bio-mimicked in this study to reduce the mechanical anisotropy in additively manufactured lattice structures. The lattice structure was printed using an elastic-plastic material (hard) that was similar to the enamel via a MEX process and toughened by an underlying soft polyurethane foam, similar to the dentin in the human tooth. Global close-sea urchin lattice structures were used to entrap the soft materials within the lattice structure. This bioinspired architecture was named the architectured lattice structure. It was 3D printed through a hybrid MEX process. The reduction of mechanical anisotropy in the printed parts was evaluated using the 3D printing of the architectured lattice structure in 0 degrees, 45 degrees, and 90 degrees orientations to the loading direction. Crash force analysis reveals that the archi-tectured lattice structures outperformed their counterpart in terms of energy absorption and crash force effi-ciency. The scanned electron microscope analysis of both designs revealed that interlayer delamination was the primary failure mechanism. Mechanical anisotropy was almost eliminated owing to the print direction and the load versus deformation curve exhibited similar mechanical behavior for all print directions. Finally, the effect of the underlying foam inside the lattice structure, which exhibited near-isotropic behavior, was evaluated via numerical analysis. The proposed bioinspired architectured lattice structures can be utilized for lightweight additively manufactured structures with high strength, toughness, and uniform mechanical properties in all directions.